Code division multiple access (CDMA), and particularly direct sequence CDMA, is a technique for spread-spectrum digital communications used for many applications, including, for example, mobile communications. In direct sequence CDMA, data signals are combined with a spreading waveform in the form of a pseudo-random-noise (PN) code to form a coded signal for transmission. The code has a frequency (i.e., the chip rate) which may be a multiple of the frequency (i.e., the bit-rate or symbol-rate) of the data signal, so that an effect of combining the data signal and the spreading waveform is that the bit period is divided into smaller chip periods. At the receiver, the signal is combined with the same spreading code to extract the data signal. The technique provides high data capacity by spreading signal energy over a wide bandwidth to increase bandwidth utilization and reduce the effects of narrow band interference. In direct sequence CDMA, the spreading code of the transmitter and receiver should be synchronized within as little as one chip period to achieve reliable communication. Multipath effects make synchronization more difficult since the wireless channel from a base station to a reception device may have several paths of different time-delays which may vary due to the movement of the reception device.
One problem with receiving CDMA signals, and in particular, wide band CDMA (WCDMA) signals, is that the data-rate of some channels may be fixed (i.e., having a predetermined spreading factor) while the data rate or other channels may vary because the spreading factor may vary significantly. Processing these different data-rate signals may be done either with software within a digital signal processor (DSP) for example, or with hardware. Processing these signals with software may consume significantly more power than processing these signals directly in hardware, however processing these signals with software may require less space/area than hardware processing may require and also may provide more flexibility. This tradeoff between power consumption and space is particularly important for portable communication devices, particularly wireless communication devices which desire to be both smaller and consume less power.
Thus, there is a general need for a method and receiver that helps balance the tradeoff between hardware and software for processing spread spectrum signals. There is also a need for a method and receiver that more efficiently processes spread spectrum signals. There is also a need for a method and receiver that more efficiently processes WCDMA channels. There is also a need for a method and receiver for processing fixed rate as well as multi-rate channels. There is also a need for a method and receiver suitable for portable communication devices.